Overall I just think software RAID is unbeatable in pretty much every aspect except pure, on paper, performance.
I will say that my one concern is that if you look at the website for the software based RAID you listed, it doesn't talk about the hardware requirements up front.
If someone is into all of it, then it will take some digging through forums and asking some pretty stupid newbie questions. Especially if you are looking for something wtih some expandability. Can I just use my existing PC and case? Do I need to buy a whole new PC? What software do I need to be running to get it up and working?
These are the exact types of questions which should be answered up front on their website, but they tend to focus more on their product and not the backbone which their product exists on, and this concerns me. Just some 'examples' would be great to see.
If I were a more low end user, then perhaps a few drives in my existing PC would be fine. But, if the RAID is something of a resource hog, then it may not play nice on my PC while I'm trying to actually USE my PC. That would be frustrating.
If I need to buy a whole new PC, then that may make sense if I need a lot of room for expansion, or have a specific goal. If I can use an old PC (and have one), then that may work just fine as well.
I've very seriously considered, and still am considering, this exact track as I really do want a 20+ drive RAID setup at some point. So, when I finish my setup of my 5th Thecus (yes, five!) I will likely try something like this.
But, when I'm wandering around in the dark, with solutions that are complex, and very little normal English explanations of decent products, the Thecus really has been a great product for me. Their manual was on a CD, but was about 100 pages with screen shots of Windows to walk me through every step of the setup. It came with software that did what it was supposed to do (awesome!) and even firmware updates were easy. Most of all, the units exist on their own. They don't steal my PC resources for their use and they have been working well.
Both solutions seem like they are good, but there definitely is a bit of a learning curve on the software solution I think.